Officials in Thailand have raised the death toll from a series of car bombings in the restive south of the country to 14 people, and said more than 340 people were injured.

Saturday's blasts targeted a hotel in the city of Hat Yai that is popular with tourists and shoppers in the town of Yala in attacks about an hour apart.

General Priewpan Damapong, the national police chief, said on Sunday that investigators believed the attacks were linked.

"It was a car bomb and it's related to the incident in Yala and I believe that it was the work of the same group," he said in televised remarks.

Colonel Pramote Promin, a spokesman for the southern army region, also said the attacks were similar.

"The incident in Yala and Hat Yai are similar in terms of the type of operation and the period of time," he said on TNN24 television, a Thai broadcaster. "In the south there are not many insurgent groups who operate like this."

The earlier attack in Yala, in which two car bombs exploded, killed 11 people and injured 110 others.

In Hat Yai, a car bomb in the basement caused a fire which spread to a shopping mall within the Lee Gardens Plaza Hotel and killed three people, including a Malaysian tourist, according to authorities.

Puwadon Wiriyawarangkun, a local police lieutenant said the explosion killed three people and caused about 230 injuries, mostly from smoke inhalation.

Hat Yai and Songkhla province have been mostly untouched by violent unrest in southern Thailand that has claimed thousands of lives in the neighbouring Muslim-dominated provinces of Yala, Pattani and Narathiwat since 2004.

Deadliest in years

Saturday's attacks, however, were the region's deadliest in recent years. Nine people were killed by a bomb in a village in Yala province last year, while 10 people died in a string of shootings there in 2007.

"There is no hint why they did this at this time," Colonel Khomgrit Srisong, the chief of Hat Yai police, told the AFP news agency by telephone. "We're questioning witnesses and the injured for more information."

Armed groups in the south of Thailand are fighting against what they perceive as a long history of discrimination against ethnic-Malay Muslims by successive Thai governments.

Struggling to quell the unrest, authorities have imposed emergency rule in the region, which rights campaigners say effectively gives the army legal immunity.

The military has admitted that troops shot dead four Muslim villagers on their way to a funeral due to a "misunderstanding" in late January after apparently fearing they were under attack by anti-state agents.

One of the region's deadliest incidents occurred on October 25, 2004, when seven people were shot dead as security forces broke up a protest in the town of Tak Bai.

Seventy-eight more people suffocated or were crushed to death in lorries while being transported to a detention centre.

Rights groups have said the failure of Thai authorities to hold security forces to account over the deaths has fuelled further violence and alienation in the southern region.